The present invention relates to a color cathode ray tube, and, more particularly, to a color cathode ray tube which can reduce deflection electric power and has improved focusing characteristics to increase the resolution of a display image on the color cathode ray tube.
A color cathode ray tube generally has a panel, a funnel connected to this panel, and a vacuum envelope comprised of a stem which is welded to the end of the cylindrical neck of the funnel. Disposed in the neck of the funnel is an electron gun assembly that emits three electron beams. Those electron beams are deflected by magnetic fields, which are generated by horizontal and vertical deflection coils of a deflection yoke mounted on the funnel, to be directed via a shadow mask toward a phosphor screen which is comprised of a three-color phosphor layer and provided on the inner surface of the panel. As this phosphor screen is scanned horizontally and vertically with the electron beams, a color image is displayed.
Of such color cathode ray tubes, a currently leading one is an in-line type which emits a line of three electron beams that pass the same plane of the electron gun, and, what is more, a self-convergence type which generates a pin-cushion magnetic field from the horizontal deflection coil of the deflection yoke and a barrel magnetic field from the vertical deflection coil and can converge a line of three electron beams on anywhere on the screen without any compensation circuitry is widely put to a practical use.
Generally, about 35% of the electric power consumed by a color cathode ray tube is horizontal deflection electric power, about 10% is vertical deflection electric power and about 45% is consumed by the deflection yoke. To decrease the power consumption of color cathode ray tubes, therefore, it is most effective to reduce the power consumption of the deflection yoke.
One way of reducing the power consumption is to make the neck to be attached to the deflection yoke thinner to place the horizontal and vertical deflection coils closer to the electron beams.
FIG. 1 shows a relationship between the outside diameter of the neck and the horizontal deflection electric power in a typical color cathode ray tube with a deflection angle of 90xc2x0 and the neck""s outside diameter of 29.1 mm. As indicated by a straight line 1 in FIG. 1, the horizontal deflection electric power is substantially increased in proportion to the neck""s outside diameter, and making the neck""s outside diameter to 22.5 mm can reduce the horizontal deflection electric power to about 80% of what is consumed in a case of the neck having an outside diameter of 29.1 mm.
With the deflection angle being the same, the overall length of a color cathode ray tube gets longer as the screen size becomes larger. In general, the overall length of a color cathode ray tube is made shorter by increasing the deflection angle which however results in increased deflection electric power. With the neck""s outside diameter of 29.1 mm, for example, setting the deflection angle to 100xc2x0 increases the horizontal deflection electric power to 135% of the power consumed when the deflection angle is 90xc2x0, as indicated by a point 2 in FIG. 1. With the neck""s outside diameter of 22.5 mm, however, even when the deflection angle is set to 100xc2x0, an increase in horizontal deflection electric power can be suppressed to 108% of the power consumed in the case of the deflection angle of 90xc2x0, as indicated by a point 3 in FIG. 1.
The aforementioned increase in deflection electric power not only leads to an increase in consumed energy but also raises the following problems. Particularly, for a tube with a deflection angle of 90xc2x0 and deflection electric power greater than 110% of the deflection electric power of the standard tube with the neck""s outside diameter of 29.1 mm, the cost for the circuitry which maintains the reliability of the deflection power supply circuit, such as the breakdown voltage characteristic and temperature characteristic, is increased significantly. Further, the leak magnetic field from the deflection yoke increases, which requires an improvement on the performance of a device which suppresses this increase. Those two problems lead to an increase in the overall cost of the apparatus that drives a color cathode ray tube. Furthermore, as the amount of heat generated by the iron loss and copper loss of the deflection yoke increases, it is necessary to enhance the heat generating characteristic of the deflection yoke itself. This leads to enlargement of the deflection yoke and an increase in the number of members used therein.
In view of the above, it is desirable to suppress an increase in deflection electric power to 10% or less of the power consumption of the standard tube, and with a deflection angle of 100xc2x0, the outside diameter of the neck should desirably be set to 23.2 mm or smaller.
Reducing the neck""s outside diameter limits the number of potentials to be supplied to the electrodes of the electron gun disposed in the neck so that the desired focusing performance will not be exhibited, resulting in an insufficient resolution.
In other words, the aforementioned, self-convergence in-line type color cathode ray tube generates non-uniform magnetic fields, a pin-cushion type horizontal deflection magnetic field and a barrel type vertical deflection magnetic field, the electron beams are affected by the deflection defocusing to form deformed beam spots on the peripheral portion of the screen, thus reducing the resolution. To overcome this problem, the self-convergence in-line type color cathode ray tube uses a dynamic focusing electron gun which changes the focusing voltage for the electron gun in synchronism with the deflection of the electron beams and apply the changed voltage to the multi-pole lens that is formed by the electron gun to thereby compensate for the deflection difference.
FIG. 2 shows a typical dynamic focusing electron gun. This electron gun comprises three cathodes KB, KG and KR for generating three electron beams in a line to cause light rays emitted from the three-color phosphor layer which constitutes the phosphor screen, three heaters HB, HG and HR for respectively heating the cathodes KB, KG and KR, an integral assembly of a first grid G1, a second grid G2, a third grid G3, a fourth grid G4, first and second segment electrodes G51 and G52 of a fifth grid G5 and a sixth grid G6 which are arranged in the named order from the cathodes KB, KG and KR toward the phosphor screen, and a shield cup C attached to the sixth grid G6.
A voltage obtained by superimposing a video signal on a DC voltage of about 150V is applied to the three cathodes KB, KG and KR via three respective conductive wires 7 provided at a stem 6 which seals the end portion of a neck 5, and a heater voltage of about 6.3V is applied to the three heaters HB, HG and HR via two respective conductive wires 7. A ground potential or a potential close to the ground one is applied to the first grid G1 via one conductive wire 7. A voltage of 500V to 900V is applied via one conductive wire 7 to the second grid G2 and the fourth grid G4, which are connected together in the tube. A focus adjusting voltage of 6 KV to 9 KV which adjusts the focus states of the electron beams is applied via one conductive wire 7 to the first segment electrode G51 of the fifth grid G5. A dynamic focusing voltage, obtained by superimposing a voltage which varies in synchronism with the deflection of the electron beams on a DC voltage of 6 KV to 9 KV, is applied via one conductive wire 7 to the second segment electrode G52 which is connected to the third grid G3 in the tube. The application of the dynamic focusing voltage changes the strength of the multi-pole lens formed between the second segment electrode G52 and the first segment electrode G51 and the strength of the main lens formed between the second segment electrode G52 and the sixth grid G6, thereby adjusting the focus states of the electron beams and, at the same time, compensating for the deflection defocusing that is produced by the deflection magnetic field in synchronism with the deflection of the electron beams. A voltage of about 25 KV is applied to the sixth grid G6 via the anode terminal provided in the funnel, an inner conductive film 8 coated on the inner surface of the funnel and a bulb spacer 9 which is attached to the shield cup C and abuts on the inner conductive film 8.
Apparently, the color cathode ray tube that is equipped with such a dynamic focusing electron gun requires nine types of voltages to be supplied to the electron gun via the conductive lead pin segments 7 provided in the stem 6.
A conventional stem for the neck""s outside diameter of 29.1 mm has ten conductive lead pin segments and can use two of them to supply the focus adjusting voltage and the dynamic focusing voltage. A stem for the neck""s outside diameter of 22.5 mm however has only eight conductive lead pin segments and is unable to supply the dynamic focusing voltage. Making the neck thinner cannot therefore improve the focusing performance of the electron gun sufficiently, disabling acquisition of the desired resolution.
As one solution to this problem, the number of conductive lead pin segments may be increased without changing the layout diameter of the conductive lead pin segments arranged on the same circumference. Increasing the number of conductive lead pin segments however results in an incompatibility with other types of color cathode ray tubes and impairs the general-purpose designing capability.
Jpn. Pat. Appln. KOKAI Publication No. 8-148103 discloses, as another solution, a method of making the inside diameter of the neck to 19.1 mm to 23.1 mm and the layout diameter of the conductive lead pin segments of the stem to 12.2 mm to 15.3 mm.
Since the thickness of the neck generally made of glass should be 2 mm or thicker in view of the breakdown voltage characteristic and the mechanical strength, the outside diameter of the neck becomes 23.1 mm to 27.1 mm according to this method. With regard to reduction of the deflection electric power, in the aforementioned case of the deflection angle being 100xc2x0, an increase in horizontal deflection electric power becomes equal to or greater than 10% of the power consumption of the tube. The reduction in the consumed power of the color cathode ray tube is insufficient.
Jpn. Pat. Appln. KOKAI Publication No. 10-83781 describes a problem of producing cracks in the stem-neck weld when a stem for the standard diameter of 15.24 mm in a case where conductive lead pin segments are laid in a stem for a neck""s outside diameter of 29.1 mm is welded to a neck whose outside diameter is smaller than 29.1 mm. This publication discloses a method of overcoming this problem by locally increasing the inside diameter of the neck in order by making the stem-welding portion of the neck thinner to thereby provide a gap of 2.1 mm between the projections surrounding the inner lead pin segments and the inner wall of the neck.
This method however lowers the mechanical strength of the neck, making the neck easier to break or making it easier to produce cracks therein. This leads to a lower reliability, such as the degree of vacuum becoming lower during operation of the color cathode ray tube and an abnormal current flowing in the power supply circuit due to the discharge in the tube, damaging the display apparatus.
Jpn. Pat. Appln. KOKAI Publication No. 58-32327 discloses a way of preventing cracks on the weld between the neck and the stem, which is accomplished by widening the gap between the projections surrounding the inner lead pin segments and the inner wall of the neck by making the layout diameter of the inner lead pin segments of the stem smaller than the layout diameter of the outer lead pin segments.
This publication however fails to specifically describe how to widen the gap between the projections surrounding the inner lead pin segments and the inner wall of the neck without impairing the reliability of the cathode ray tube.
As mentioned above, to decrease the power consumption of a color cathode ray tube, it is effective to reduce the power consumption of the deflection yoke by making the neck thinner to position the horizontal and vertical deflection coils of the deflection yoke closer to the electron beams. A dynamic focusing electron gun which has an excellent focusing characteristics can provide a high resolution. If the neck of this gun is made thinner, the number of potentials to be supplied to the dynamic focusing electron gun becomes insufficient, so that the resolution cannot be improved.
As one solution to this problem, the conductive lead pin segments in the stem may be increased without changing the layout diameter of the conductive lead pin segments. Increasing the number of conductive lead pin segments however results in an incompatibility with other types of color cathode ray tubes and impairs the general-purpose designing capability.
Another solution has been proposed, which makes the inside diameter of the neck to 19.1 mm to 23.1 mm and the circular layout diameter of the conductive lead pin segments of the stem to 12.2 mm to 15.3 mm. The thickness of the neck generally made of glass should be 2 mm or thicker in view of the breakdown voltage characteristic and the mechanical strength. It is pointed out that in this case, the neck then would have an outside diameter of 23.1 mm to 27.1 mm, which results in an insufficient reduction in the consumed power of the color cathode ray tube.
To avoid cracks in the stem-neck weld when a stem for the standard diameter of 15.24 mm in a case where conductive lead pin segments are laid in a stem for a neck""s outside diameter of 29.1 mm is welded to a neck whose outside diameter is smaller than 29.1 mm, a method of locally increasing the inside diameter of the neck by making the stem-welding portion of the neck thinner has been proposed. This method however decreases the mechanical strength of the neck, making the neck easier to break or making it easier to produce cracks therein.
As a solution to such production of cracks on the weld between the neck and the stem, there has been proposed a method of widening the gap between the projections surrounding the inner lead pin segments and the inner wall of the neck by making the circular layout diameter of the inner lead pin segments of the stem smaller than the circular layout diameter of the outer lead pin segments. This proposal however fails to include a specific description of how the gap between the projections surrounding the inner lead pin segments and the inner wall of the neck is widened without impairing the reliability of the cathode ray tube.
Accordingly, it is an object of the present invention to provide a reliable, low-power-consumption and high-resolution color cathode ray tube which has deflection electric power reduced by making the neck thinner and has improved focusing characteristics for electron beams and a compatibility with other types of color cathode ray tubes.
(1) In a color cathode ray tube comprising a stem structure whose stem seals the end portion of the neck of a funnel constituting an vacuum envelope and is welded to the neck, an exhaust tube provided integrally on the center axis of the stem structure and led out of the end portion of the neck, a plurality of conductive wires which include inner lead pin segments electrically insulated from one another and penetrating the same circumference around the center axis of the stem structure to be positioned inside the neck, and outer lead pin segments positioned outside the end portion of the neck, and which supply voltages to be applied to the heaters, cathodes and a plurality of electrodes of an electron gun assembly placed in the neck, and projections provided integrally on the stem structure and surrounding those portions of the inner lead pin segments which are positioned near the stem structure, at least a part of each conductive wire is bent in the associated projection, the bent portion of this conductive wire is directed outward in the radial direction of the stem with respect to the center axis of the projection, and the diameter of the first circumference along which the inner lead pin segments are arranged is set smaller than that of the second circumference along which the outer lead pin segments are arranged.
(2) In the color cathode ray tube as recited in paragraph (1), the diameter of the first circumference is set smaller than that of the second circumference by 0.3 mm to 2.2 mm.
(3) In the color cathode ray tube as recited in paragraph (1) or (2), the diameter of the first circumference is set within a range of 12.8 mm to 14.7 mm and the diameter of the second circumference is set within a range of 15.0 mm to 15.5 mm.
(4) In a color cathode ray tube comprising a stem structure whose stem seals the end portion of the end portion of the neck of a funnel constituting an vacuum envelope and is welded to the neck, an exhaust tube provided integrally on the center axis of the stem structure and led out of the end portion of the neck, a plurality of conductive wires which include inner lead pin segments electrically insulated from one another and penetrating the same circumference around the center axis of the stem structure to be positioned inside the neck, and outer lead pin segments positioned outside the end portion of the neck, and which supply voltages to be applied to the heaters, cathodes and a plurality of electrodes of an electron gun assembly placed in the neck, and projections provided integrally on the stem structure and surrounding those portions of the inner lead pin segments which are positioned near the stem structure, at least a part of each conductive wire is bent in the associated projection, the bent portion of this conductive wire is directed outward in the radial direction of the stem with respect to the center axis of the projection, the diameter of the first circumference along which the inner lead pin segments are arranged is set smaller than that of the second circumference along which the outer lead pin segments are arranged, and a gap between each of the projections and the inner surface of the neck at a middle of the height of that projection with a curved portion or an inflexion portion of the inner surface of the stem structure, which extends toward the exhaust tube from the projection, taken as a reference is set equal to or greater than 0.5 mm.
(5) In a color cathode ray tube comprising a stem structure whose stem seals the end portion of the end portion of the neck of a funnel constituting an vacuum envelope and is welded to the neck, an exhaust tube provided integrally on the center axis of the stem structure and led out of the end portion of the neck, a plurality of conductive wires which include inner lead pin segments electrically insulated from one another and penetrating the same circumference around the center axis of the stem structure to be positioned inside the neck, and outer lead pin segments positioned outside the end portion of the neck, and which supply voltages to be applied to the heaters, cathodes and a plurality of electrodes of an electron gun assembly placed in the neck, and projections provided integrally on the stem structure and surrounding those portions of the inner lead pin segments which are positioned near the stem structure, at least a part of each conductive wire is bent substantially in the associated projection, the bent portion of this conductive wire in the projection is directed outward in the radial direction of the stem with respect to the center axis of the projection, the diameter of the first circumference along which the inner lead pin segments are arranged is set smaller than that of the second circumference along which the outer lead pin segments are arranged, the diameter of each projection at a middle of the height of that projection with a curved portion or inflexion portion of the inner surface of the stem structure, which extends toward the exhaust tube from the projection, taken as a reference is set equal to or greater than 2.5 mm, and a gap between each projection and the inner wall of the neck at a middle of the height of that projection is set equal to or greater than 0.5 mm.
(6) In the color cathode ray tube as recited in paragraph (4) or (5), the diameter of the first circumference is set within a range of 12.8 mm to 14.7 mm, the diameter of the second circumference is set within a range of 15.0 mm to 15.5 mm and the inside diameter of the neck is set within a range of 17.8 mm to 19.2 mm.
(7) In the color cathode ray tube as recited in paragraph (4) or (5), the diameter of the first circumference is set within a range of 12.8 mm to 14.7 mm, the diameter of the second circumference is set within a range of 15.0 mm to 15.5 mm, the inside diameter of the neck is set within a range of 17.8 mm to 19.2 mm and the outside diameter of the neck is set within a range of 21.8 mm to 23.2 mm.
(8) In the color cathode ray tube as recited in paragraph (4) or (5), each conductive wire is thinner than at least one of the inner pin segment and the outer pin segment.
(9) In the color cathode ray tube as recited in paragraph (4) or (5), a bent portion of each conductive wire is located in the respective projection by an amount ranging from 10% to 50% of the height of the projection with a curved portion or an inflexion portion of the inner surface of the stem structure, which extends toward the exhaust tube from the projection, taken as a reference.
(10) In the color cathode ray tube as recited in paragraph (4) or (5), there are nine or more conductive wires.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.